U.S. Pat. Nos. 5,736,173 and 6,569,370 disclose a preform injection mold including a stripper plate that supports a wear plate on its upper surface. Opposed slide bars, having neck rings mounted thereon, are slidably supported by the wear plate.
U.S. Pat. No. 6,450,797 discloses molding apparatus including a pair of slide bar inserts that are laterally movable into and out of engagement with other mold components.
U.S. Pat. No. 6,799,962 discloses a stripper assembly for an injection molding machine. The assembly comprises a slide bar pair consisting of a first slide bar and a second slide bar. Transmission means is operatively coupled to the first slide bar and the second slide bar to transform movement of the first slide bar in one direction into movement of the second slide bar in an opposite direction.
FIG. 1 is a cross-sectional view through a portion of an injection mold of U.S. Pat. No. 6,569,370. Generally, the mold is shown to include a mold base 16 comprising a core plate 3, a stripper plate 17, and a cavity plate 10, having a stack 1 of molding inserts arranged therein. FIG. 1 shows the mold in a mold-closed position ready for injection of the plastic into the mold. The stack 1 includes a mold core 2 fitted into the core plate 3 and retained therein by a lock ring 4 and bolts 5. The mold core 2 contains a cooling tube 6 for the transmission of cooling fluid from a source within the core plate 3 to remove heat from the injected material in the mold cavity 7 and solidify the molded part in the mold cavity 7. The stack 1 comprises a set of complementary molding inserts including a cavity insert 8 and an adjacent gate insert 9 that are retained in the cavity plate 10 by a cavity flange 11 and bolts (not shown). Cooling channels 12 circulate cooling fluid from a source through the cavity insert 8 and gate insert 9 to remove heat from the injected material. The mold base 16 also includes a pair of slide bars 15A and 15B that are slidably supported on a wear plate 19, itself mounted on the stripper plate 17. The slide bars 15A, 15B are configured for carrying a pair of neck rings 13 and 14 of the mold stack 1 between an in-mold position and an out-mold position. The wear plate 19 is sacrificial material and reduces the wear between the slide bars 15A, 15B and the stripper plate 17 when the neck rings 13 and 14 are moved apart by the slide bars 15A, 15B to release a molded part from the mold cavity 7. Cooling channels 18 circulate cooling fluid from a source through the neck rings 13 and 14 to remove heat from the injected material. Molten material is conveyed to the mold cavity via a hot runner nozzle, hot runner manifold and hot runner stacks.
FIG. 2 is a partial perspective view of a known slide bar and stripper assembly that may be used with the stack 1 of FIG. 1. In this assembly, the slide bars 21A and 21B are linked to the mold by a connecting structure 61 that includes connecting bars 22A and 22B, respectively, and a pair of gibs 23A and 23B bolted to the stripper plate 25, for slidably arranging the connecting bars 22A and 22B in a guide that is preferably provided as a groove 26 configured in the stripper plate 25. The connecting bars 22A and 22B travel along the stripper plate groove 26 to activate the slide bar 21A and 21B, between an in-mold and an out-mold position, to open and close the neck rings in the mold. For purposes of illustration, a single pair of neck rings 20A and 20B is shown. Wear plates 27, 28 are located between the slide bars 21A and 21B and the stripper plate 25 to reduce wear of the slide bars 21A and 21B and stripper plate 25. Because the wear plates 27, 28 do wear, clamping force cannot be reliably applied therethrough but instead passes along the mold stack. When the clamping force A (see FIG. 1) going through mold stack 1 becomes so high that it could start to wear stack components, it becomes necessary to add clamping force blocks 29, shown with reference to FIG. 1, outside the immediate area of the mold cavities to take excess clamping force.
As shown in FIG. 2, in the prior art, gibs 23A, 23B are attached to the stripper plate 25 to constrain the connecting bars 22A and 22B within the groove 26. The gibs 23A, 23B are made from a stiff material such as an aluminum-bronze extruded bar stock sold under the registered trade mark ‘Ampco 18’ by Ampco Metal S. A. Corp of Switzerland (i.e. Young's Modulus of about 117 GPa). When the connecting bars 22A and 22B are moved along the groove 26, a corresponding movement of the slide bars 21A and 21B, linked thereto, between the in-mold and the out-mold positions, causes the neck rings 20A and 20B, respectively, to move between an open and a closed configuration. The connecting bars 22A and 22B are moved along the channel by a cam arrangement, not shown, or by any other suitable means that may be apparent to those skilled in the art. The wear plates 27, 28 between the slide bars 21A and 21B and the stripper plate 25 separate the stripper plate 25 from the slide bars 21A and 21B to prevent wear of the confronting surfaces of the slide bars 21A and 21B and stripper plate 25. However, the existence of this wear plate 27, 28 does not provide for a reliable application of clamping force between the slide bars 21A and 21B and the stripper plate 25 once the wear plate becomes worn.